The effects upon speed and power performance by a propeller in poor surface condition are difficult to assess in practice.

Some years ago British Ship Research Association (BSRA) developed an integrated system of analytical procedures for modelling propeller characteristics in real flow conditions behind ships' hulls.The following case studies are based on BSRA's analytical program. Calculations have been made on a fuel price of USD $185 per tonne.

    • A 10 year old 320.000 DWT crude oil carrier trading between Arabian Gulf and Europe.
    • Speed 12-13 knots (cargo/ballast).
    • The propeller is four bladed (fixed pitch).
    • Engine: Steam turbine main propulsion plant.

    • New building: 45.000 DWT bulk carrier, trading between the Mexican Gulf and Japan.
    • Speed 13 knots.
    • With a four bladed fixed pitch propeller.
    • Engine: Diesel main propulsion plant.

    • A 12 year old, 1600 TEU capacity container feeder, operating in the North Atlantic.
    • Operating at an average speed of 19 knots (three knots below design speed).
    • Fitted with a five bladed pitch propeller.
    • Engine: Steam turbine or slow speed diesel main propulsion plant.

In the table below, the results from the BSRA analysis method have been used for calculating the cost in annual terms of excessive roughness relative to Rubert Grade A (highest smoothness practically achievable, for definitions see Roughness Definitions).

Rubert Grade Cost of propeller roughness relative to Rubert Grade A ($ per annum)
Constant speed operation
Constant power operation
Ship A
Ship B
Ship C
Ship A
Ship B
Ship C
B*
15 000
3000
5000
10 000
3000
10 000
C
54 000
14 000
24 000
36 000
13 000
48 000
D
106 000
32 000
55 000
71 000
29 000
109 000
E
155 000
52 000
88 000
103 000
48 000
174 000
F*
205 000
70 000
122 000
135 000
62 000
240 000
* Approximate
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